7

This kit is a FM receiver built in 1977 by DK0TV. The receiver works on a single fixed frequency 30.000 MHz FM and has a very good sensitivity. It is used with a 10 GHz Gunnplexer to listen to the 3 cm band with a 30 MHz intermediate frequency. Here are details on how it works: The input at 30 MHz is amplified by a dual gate MOSFET The S042P is a mixer with ...


6

As mentioned in the comment by henryflower, make sure that the shaft (and thus the frame) of the variable capacitor are grounded. You need to use rubber mounting grommets around the screws which bolt the tuning capacitor to the PCB or chassis. Then run one thick wire from the frame of the tuning capacitor from a point away from the front panel to one point ...


4

Circuit looks OK. Note that the highest impedance point in this circuit is near the box open end. RF voltage here is highest in this oscillator, and is susceptible to coupling out the top. A shield lid (soldered to the box) should help.


4

I think I figured this out. By looking at VFO with an oscilloscope I could catch a brief glitch (~1.5ms) in the signal when the frequency is changed: It was hard to notice because you can't easily trigger on this. I had to manually trigger single captures while tuning for some time to see this. Then by googling "si5351 output glitches" I've found ...


3

Antenna tuners use fairly standard 250 V relays, so this would be a good place to start. The SGC-230 is an example I know. This post has some nice photos of its relays. Smaller tuners use little black relays, if you scratch around for photos you might be able to read the specifications printed on the relays. The SGC-235 is a claimed 400 watt tuner. If I ...


3

Try powering the LM386 temporarily off a battery. if the popping stops, then the cause is a surge being conducted into the 386 from the supply that feeds the rest of your circuit. Normally, you would bypass the power input of the 386 to ground with a hefty electrolytic capacitor (50 to 100mfd) and then shunt that with a fast-acting cap (0.01 to 0.1uF) to ...


3

After a little bit of searching I discovered that this topology is called QER filter, where QER stands for Quasi-EquiRipple. This topology is attributed to Dr. Dave Gordon-Smith, G3UUR, who is also well-known for inventing a popular method (the G3UUR method) of measuring crystals. Apparently it was first described in The QRP Quarterly, Spring 2010 under the ...


2

Alan Wolke, W2AEW, explained this topic very well in one of his videos: Measuring Crystals with NanoVNA and other tools. Alan shows several methods. Personally, I measure: C0: directly with a suitable RLC-meter. If you don't have one or are in a hurry, assume 2.5 pF, that will be good enough. VNA can be used for the task if it's capable to measure the ...


2

C (E) = I (t) E= I (t) / C C = Capacitance in uF E = Ripple Voltage, p-p I = Max Load in mA t = "7.5mSec" for 60Hz line Vpeak (.707) = Vrms Vp-p = Vrms (1.414) THEN, E = I (t) / C (in Vp-p) Then, Vrms = Vp-p / 1.414 (Ripple Voltage p-p) SO, if C (E) = I (t) Then E = I (t) /C Trans Vrms * 1.414 * 0.9 = No Load D.C. Ripple Voltage Vrms / ...


1

Since it happens when switching frequencies, I suspect glitches of some form in the local or beat frequency oscillators' output. The mixers simply multiply the "signal" by the oscillator. Any noise or glitch in the oscillator outputs will be reflected in the mixed outputs. You may be more sensitive to BFO glitches, since the output is at DC, not a ...


1

The most likely answer without measurements or schematics is that you transponders are connected to earth by the coupling Capacitance of water , while the common mode of a floating battery to an unbalanced electronic circuit has more antenna effects pickup up one side of the battery terminal circuit (0V gnd plane) than the other from high E-field line ...


1

I used Hongfa HFD27/012-S and HFD2/012-S-L2 in several projects for... well, everything RF, including bypassing the 5-10W PA (don't use them for DC though!). These are 12V relays, but you can easily find 5V ones with similar ratings - 1A 125VAC / 2A 30VDC. To my knowledge, there is no much to consider. I had only two problems with relays. Firstly, one relays ...


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